Device for improving the error curves of induction type meters with several driving elements



July 12, 1955 G. J. THEVENON 2,713,148

DEVICE FOR IMPROVING THE ERROR CURVES OF INDUCTION TYPE METERS WITHSEVERAL DRIVING ELEMENTS Filed July 30, 1951 2 Sheets-Sheet l Fig.1 12

INVENT R Q. J Ucvcmn RT'TOHNEyS 9' July 12, 1955 G. J. THEVENON2,713,143

DEVICE FOR IMPROVING THE ERROR CURVES OF INDUCTION TYPE METERS WITHSEVERAL DRIVING ELEMENTS Filed July 30, 1951 2 Sheets-Sheet 2 Fig.4

Fig.3

. I 52 |H I l I 53 INVE/VTO- I hTTamvzys 1/ United tates Patent 0 6(Ilaims. (Cl. 324--137) Numerous devices are known for improving, atheavy loads, the error curves of single phase induction type meters.These devices most frequently consisting of a magnetic part (shunt)placed in shunt on the main flux set up by the current electromagnet,are dimensioned so as to become saturated at a predetermined value Is ofthis current, so that when the current exceeds this value, an additionaltorque appears for compensating the bralc'ng torque generated by themain flux set up by the current electro-rnagnet.

Ft/"hen dealing with polyphased meters with multiple driving elements,and, in particular, with three-phase meters, the compensation obtainedis much less satisfactory. lt is possible to dimension the shunts forobtaining the desired compensation on the error curve, in three phase,balanced loads, but an undesirable hypercompensation is then obtained ofthe error curves of each one of the driving elements consideredseparately.

Obviously, one may be content with dimensioning the shunts for obtaininga correct compensation of each one of the driving elements takenseparately, but the compensation obtained is distinctly insufiicient forthe error curve recorded with three phase, balanced loads.

The object or the present invention is a device for improving the errorcurves of induction type meters with several driving elements, at heavyloads, while considerably reducing the deviation between the mean of theerrors read on each driving element considered separately and the errorread with polyphase current, all the driving elements being under equalloads.

This device is characterized in that at least one of the drivingelements is provided with an auxiliary pole piece, placed on the axis ofsymmetry of the current and voltage electro-rnagnets of said drivingelement, said auxiliary pole piece being provided with a winding throughwhich fiows a current produced by an electromotive force induced in asecond winding and proportional only to the magnetic flux set up by thewindings of the current electro-magnet of another driving element, thewhole being so arranged that the interaction of the magnetic flux causedby said auxiliary pole piece with the magnetic flux set up by thewindings of the current electro-magnet of the driving element comprisingsaid auxiliary pole piece, generates a torque which adds to the torquegenerated by the driving elements of the meter.

The invention will be more clearly understood from the followingdescription, when read with reference to the appended drawings, saiddescription and drawings being, of course, given chiefly by way ofindication and having no limitative meaning.

Figure 1 shows an induction type meter with two driving elements, whichis provided with the device according to the invention.

Figure 2 shows an induction type meter with two driving elements, whichis provided with two devices according to the invention.

Figure 3 shows an induction type, three phase meter 2,713,143 PatentedJuly 12, 1955 with three driving elements, in which the device accordingto the invention has been incorporated.

Figure 4 illustrates a particular type of embodiment of one of thefeatures of the invention.

In Figure 1, 10 and 11 are two driving elements of a well known type,used in the construction of a three phase meter, for instance. Each oneof these driving elements comprises respectively a central voltage polepiece 12 and 13, and two current pole-pieces 4344 and IS-46. The twodiscs, not shown, are placed respectively in the air gaps includedbetween the pole pieces 12 and 43--44 on the one hand, 13 and 45-46 onthe other hand. The current windings are illustrated at 47, 48 and 49,5t and the voltage windings at 51, 52.

According to the invention, a soft steel tongue element 16, forming anauxiliary pole piece, is arranged between the two current pole pieces 43and i4 and along the axis of the central voltage pole piece 12 of thedriving element it}. A winding 17 is placed on this tongue 16. Thiswinding is closed on another winding 18, wound between the two currentpole pieces 45 and 46 and along the axis of the central voltage polepiece 13 of the driving element 11.

The tongue 16 forms part of a member 19 which is secured on the drivingelement It!) at two points which are at the same magnetic potential.

An electromotive force e2 is produced in the winding 18 when currentflows through the windings 49 and 53 of the pole pieces 45 and 46. Thiselectromotive force is proportional only to the flux 2 caused by thewindings 49 and 50 of the pole-pieces 45 and 46. The flux produced bythe voltage coil 52 of the central voltage pole piece 13 does not act inthe winding 18, in particular, due to its symmetrical arrangement betweethe two current pole pieces 45 and 46 in the portion AD of the magneticcircuit of the electro-nagnet 11. This electromotive force e2 gives riseto a current is in winding 17. The flux (p2 produced by this current iscoaxial with the main flux produced by the voltage coil 51 of thecentral voltage pole piece 12, due to the position of the tongue 16 onthe axis of said voltage pole piece. Under the circumstances, theextraneous torques due to the interaction of these two fluxes cancel oneanother.

The interaction of the flux oz and the flux or, proportional to thecurrent flowing through the windings 47 and 48 of the pole pieces 43 and44, generates an additional torque C which is expressed by K being aproportionality coefficient and a the angle between or and z.

The directions of the windings on 17 and 18 are such that the additionaltorque C adds with the driving torque produced by the driving element itThe ampere-turns applied to the tongue 16 are determined in such amanner that the additional torque C be just suflicient to give an exactcompensation at a given load (for instance at full load), for thebraking torques generated by the fluxes produced by the currentelectromagnets.

This compensation, once effected for a predetermined load, remains validover a wide measuring range, since the additional torque produced, beingproportional to the product of the two current fluxes, obeys the samelaw of variation as the braking torques generated by the currentelectro-rnagnets, which are proportional to the square of each one ofthe two current fluxes.

In Figure 2, the induction type meter with two driving elements isprovided with two devices according to the invention. In this figure,wherein the same numerals have the same signification as in Figure l, asoft steel tongue 26 can be seen, forming a second auxiliary pole piece,placed between the current pole pieces 45 and 46, and on the axis of thecentral voltage pole piece 13 of the lower driving element 11. Thistongue 26 forms part of a member 29 which is secured to the drivingelement 11 at two points which are at the same magnetic potential. Onthis tongue 26 is placed a winding 27 which is closed on another winding28 wound on the driving element 10, between the current pole pieces 43and 44 and on the axis of the central voltage pole piece 12.

An induction type, three phase meter, with three driving elements, canbe providedwith three devices according to the invention. Designating byH, C andB the three driving elements, the winding on the tongue placedbetween the two current pole pieces of H will be supplied, for instance,bya winding wound between the two current pole pieces of C; the windingon the tongue placed between the two current pole pieces of C will besupplied from a winding wound between the two current pole pieces of Band the winding on the tongue placed between the two current pole piecesof B will be supplied from a winding wound between the two current polepieces of H.

However, a simpler device, shown in Figure 3, can also be used in such ameter. In this figure, where H, C and B represent the three drivingelements and where 47, 48, 49, 50, 53, 54 and 51, 52, 55 arerespectively the current windings and voltage windings of H, C and B,-only the C driving element is provided with a tongue 31, forming anauxiliary pole piece, placed between its two current pole pieces, and onthe axis of the central voltage pole piece. Two windings, 32 and 33,insulated from each other, are wound on this tongue. The winding 32 isclosed on another winding 34, wound between the two current pole'piecesof the driving element H and on the axis of its central voltage polepiece. A current in flows through the winding 32. The winding 33 isclosed on another winding 35, wound between the two current pole piecesof the driving element B, and on the axis of its central voltage polepiece. A current in flows through the winding 33.

.A resultant flux q: (in-HE) is obtained in the tongue 31, whichproduces an additional torque proportional to do. q: (in-l-in) sin a,410 being the main current flux ditional torque remains constant inmagnitude and direction..

Referring again to Figure 1, it will be noted that the tongue 16 whichforms an auxiliary pole piece, is linked with a fraction of the mainvoltage flux, so that an induced electromotive force, due to this fluxappears in the winding 17, which produces, in the circuit 1718, acirculating current proportional to this voltage flux. This currentgives rise, in718, to an extraneous flux. To avoid the interaction ofthis flux with the main voltage flux which flows through the drivingelement ,11 and, consequently, undesirable extraneous torques, it willbe convenient for this flux to be closed by a magnetic circuit having anextremely low reluctance so as to prevent it from going through the mainair-gap in which the disc rotates.

In a driving element similar to that shown in Figure 1, the extraneousflux produced by 18 will close'along the path A-E--F-G-D. Thearrangement of one or more magnetic metal bridges between A and D (theframe forming possibly part of oneof these bridges) could also becontemplated.

Figure 4 where 56 and 57 are the current windings shows a specificembodiment of the above mentioned bridge. The portion AD of the currentelectromagnet is divided into two branches 41-42 by a longitudinalaperture. The winding 18 is wound on the branch 41, for instance. Underthe circumstances, the flux which originates in' the branch 41 closessubstantially entirely in the branch 42, the reluctance of which isextremely low.

It should be'understood that the application of the device, object ofthe present invention, is not limited to the driving elements describedand illustrated, but that p it extends to any form of driving element.

What is claimed is: a

1. In an induction type meter comprising at least two driving elementseach of which includes, one voltage electromagnet comprising threepoles, and one current electromagnet comprising two poles, the poles ofsaid electromagnets defining an air gap for a conductive metal rotarydisc, a device for. improving the error curve, said device comprising afirst auxiliary pole piece placed between the two poles of said currentelcctromagnet and on the axis of the central pole of said voltageelectromagnet of the first driving element, a second auxiliary polepiece placed between the two poles of said current electromagnet and inthe axis of the central pole of the voltage electromagnet of the seconddriving element, a first electrical circuit comprising a first windingcoiled around said first auxiliary pole and asecond winding coiledaround the said current electrom'agnet of said second driving elementbetween the bases of the current poles and on the axis of the centralpole of the voltage electromagnet of said second driving element, and asecond electrical circuit comprising a first winding coiled around saidsecond auxiliary pole and a second winding coiled around thecurrentelectromagnet of said first driving element between the bases ofthe current poles and on the axis of the central pole of the voltageelectromagnet of said first driving element.

2. In an induction type meter comprising at least two driving elementseachof which includes one voltage electromagnet comprising three polesand one current electromagnet comprising two poles, the poles of saidelectromagnets defining an air gap for a conductive rotary disc, adevice for improving the error curve, said device comprising at leastone auxiliary pole placed between the two poles of said currentelectromagnet and on the axis of the central pole of the voltageelectromagnet of one of said'driving elements, a first winding coiledaround said auxiliary pole and at least a second winding coiled aroundthe current electromagnet of the otherdriving element between the basesof the current poles and on the axis of the central pole of the voltageelectromagnet of said driving element. V 3. A device according to claim'2 wherein there is provided a magnetic circuit with an extremely lowreluctance, through which closes the extraneous flux generated in thewinding coiled around the current electromagnet, between the bases ofthe current poles and on the axis of the central pole of the voltageelectromagnet, of one of said driving elements. a

4. An-induction type meter comprising at least two driving elements eachof which includes one voltage electromagnet comprising three poles andone current electromagnet comprising two poles, the poles of saidelectromagnets defining an air gap for a conductive rotary disc, oneauxiliary pole piece placed between the two poles of said currentelectromagnet and on the axis of the central pole of said voltageelectromagnet of the first of said driving elements and means forgeneratingan electromotive force by the current electromagnet only ofthe second driving element and applying said electromotive force on saidauxiliary pole piece to thereby set up in. the first driving element'anadditional magnetic field generating 5 rent electromagnet of one of saiddriving elements and placed between the bases of the current poles andon the axis of the central pole of the voltage electromagnet of saiddriving element.

6. A device according to claim 2 wherein said second winding is coiled,between the bases of the current poles and on the axis of the centralpole of the voltage electromagnet of one of said driving elements,around one of the two branches of a longitudinal aperture provided inthe magnetic circuit of said driving element and between the bases ofsaid current poles.

References Cited in the file of this patent UNITED STATES PATENTSCifirinowitsch Dec. 22,

Freeman July 1,

FOREIGN PATENTS Great Britain Jan. 7,

Germany Nov. 7,

France May 2,

Germany May 25,

